Effects of Electrolyte Solutions and their pH on the Electrochromic Cycling Stability of Reactively Sputtered WO_3 Thin Films

摘要

WO_3 thin films were prepared by reactive sputtering and their electrochromic (EC) cycling characteristics were examined in aqueous electrolyte solutions with a pH range from 1 to 6. These solutions contained H_2SO_4 and a supporting electrolyte of either, K_2SO_4 or Na_2SO_4, which was added to maintain a constant ionic conductivity. Stable EC cycling was achieved in solutions containing K_2SO_4 with pH from 1.5 to 3.6, whereas some degradation occurred in solutions containing Na_2SO_4. In neutral solutions, the WO_3 films peeled off within 20 cycles, regardless pf the type of electrolyte. A maximum transmittance change from 38 to 90%, and stable EC cycling up to 100 cycles were obtained in acidic electrolytes containing H_2SO_4 + K_2SO_4 with a pH of 1.5 to 2.5.